A multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO) antenna technology is a key technology in wireless communications. A MIMO wireless system can obtain a diversity and an array gain by transmission beamforming (Beamforming, BF)/precoding and receive signal combination. Transmission beamforming or precoding needs to use a precoding matrix. To obtain an optimal precoding matrix, a transmit end needs to completely know channel state info/nation (Channel State Information, CSI). Therefore, a receive end needs to perform quantization on instantaneous CSI and provide feedback to the transmit end. This kind of MIMO system is referred to as a closed-loop MIMO system.
For the closed-loop MIMO system, the CSI fed back by the receive end to the transmit end includes information such as a channel quality indicator (Channel Quality Indicator, CQI), a precoding matrix indicator (Precoding Matrix Indicator, PMI), and a rank indicator (Rank Indicator, RI). When the receive end feeds back the CQI on a physical uplink control channel (Physical Uplink Control Channel, PUCCH) or a physical uplink shared channel (Physical Uplink Shared Channel, PUSCH), there are various types of feedback modes. For one type of feedback mode, for a given system bandwidth, a feedback granularity of a CQI of a subband is constant.
However, when the MIMO system has a relatively large quantity of antenna ports, for example, massive MIMO (Massive MIMO), a larger quantity of antennas indicates smaller frequency selectivity of channel quality after precoding. When the quantity of the antennas is very large, a frequency of the channel quality shows a feature close to flatness. However, an existing manner of feeding back a CQI at a constant feedback granularity does not use the foregoing feature, thereby increasing system overheads.